Beam steering optics for near-eye and head mounted displays

ABSTRACT

A near-eye display system includes a display panel to present image frames to the eyes of a user for viewing. The system also includes a beam steering assembly facing the display panel that is configurable to displace a light beam incident on the beam steering assembly, thereby laterally shifting light relative to an optical path of the light beam incident on the beam steering assembly. The beam steering assembly includes a birefringent plate configurable to replicate a light ray incident on the beam steering assembly such that the replicated light ray is laterally shifted relative to an optical path of the light ray incident on the beam steering assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. patent application Ser. No. 15/889,796, entitled “BEAM STEERING OPTICS FOR VIRTUAL REALITY SYSTEMS” and filed on Feb. 6, 2018, the entirety of which is incorporated by reference herein.

BACKGROUND

Head-mounted displays (HMDs) and other near-eye display systems can utilize an integral lightfield display, magnifier lens, lenslet or pinhole array, or other viewing optics provide effective display of three-dimensional (3D) graphics. Generally, the integral lightfield display employs one or more display panels and an array of lenslets, pinholes, or other optic features that overlie the one or more display panels. The HMDs and other near-eye display devices may have challenges associated with the limited pixel density of current displays. Of particular issue in organic light emitting diode (OLED)-based displays and other similar displays is the relatively low pixel fill factor; that is, the relatively large degree of “black space” between pixels of the OLED-based displays. While this black space is normally undetectable for displays having viewing distances greater than arm's length from the user, in HMDs and other near-eye displays this black space may be readily detectable by the user due to the close proximity of the display to the user's eyes. The visibility of the spacing between pixels (or sub-pixels) is often exacerbated due to magnification by the optics overlying the display panel. Therefore, there occurs a screen-door effect, in which a lattice resembling a mesh screen is visible in an image realized in the display, which typically interferes with user immersion in the virtual reality (VR) or augmented reality (AR) experience.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference symbols in different drawings indicates similar or identical items.

FIG. 1 is a diagram illustrating an arrangement of components of a near-eye display system utilizing a beam steering assembly to project imagery in accordance with some embodiments.

FIG. 2 is a diagram illustrating a cross-section view of an implementation of the near-eye display system of FIG. 1 for providing super-resolution imagery in accordance with some embodiments.

FIG. 3 is a diagram illustrating a diffractive beam steering element for use in the near-eye display system of FIG. 1 in accordance with some embodiments.

FIG. 4 is a diagram illustrating a refractive beam steering element for use in the near-eye display system of FIG. 1 in accordance with some embodiments.

FIG. 5 a diagram illustrating another refractive beam steering element for use in the near-eye display system of FIG. 1 in accordance with some embodiments.

FIG. 6 is a flow diagram illustrating a method for sequential display of images to provide a super-resolution image display in the near-eye display system of FIG. 1 in accordance with some embodiments.

FIG. 7 is a diagram illustrating a method of generating passive super-resolution images in accordance with some embodiments.

FIG. 8 is a diagram illustrating a top-down view of a birefringent beam steering element in accordance with some embodiments.

FIG. 9 is a diagram illustrating a top-down view of another birefringent beam steering element in accordance with some embodiments.

DETAILED DESCRIPTION

FIGS. 1-9 illustrate various systems and techniques for providing optical beam steering in a near-eye display system or imaging system. As described in further detail below, a head mounted display (HMD) or other near-eye display system implements a beam steering assembly disposed between a display panel and a user's eye. The beam steering assembly can be deployed in a passive configuration to reduce or remove the screen door effect or increase perceived resolution, or in an active configuration (e.g. via time multiplexing) to increase effective resolution through exploitation of the visual persistence effects of the human eye. In some implementations, the near-eye display system projects time-multiplexed images at a higher display rate such that two or more of the images having different visual information are effectively combined by the human visual perception system into a single “super-resolution” image; that is, an image with an effective resolution higher than the native resolution of the display panel. In other implementations, the near-eye display system projects two or more adjacent images having the same visual information but are spatially shifted via the beam steering apparatus relative to each other so as to be perceived by the user as an image with light emitting elements of increased apparent size, and thus effectively covering the non-emissive portions between the light emitting elements of the display.

FIG. 1 illustrates a near-eye display system 100 for implementation in a head mounted device (HMD), heads-up display, or similar device in accordance with some embodiments. As depicted, the near-eye display system 100 includes a computational display sub-system 102. The near-eye display system 100 further can include other components, such as an eye-tracking subsystem, an inertial measurement unit (IMU), audio componentry, and the like, that have been omitted for purposes of clarity. The computational display sub-system 102 includes a left-eye display 104 and a right-eye display 106 mounted in an apparatus 108 (e.g., goggles, glasses, etc.) that places the displays 104, 106 in front of the left and right eyes, respectively, of the user.

As shown by view 110, each of the displays 104, 106 includes at least one display panel 112 to display a sequence or succession of near-eye images, each of which comprises an array 114 of elemental images 116. The display panel 112 is used to display imagery to at least one eye 118 of the user in the form of a normal image (e.g., for super-resolution implementations) or a lightfield (e.g., for lightfield implementations). In some embodiments, a separate display panel 112 is implemented for each of the displays 104, 106, whereas in other embodiments the left-eye display 104 and the right-eye display 106 share a single display panel 112, with the left half of the display panel 112 used for the left-eye display 104 and the right half of the display panel 112 used for the right-eye display 106.

As depicted, the near-eye display system 100 incudes a beam steering assembly 120 overlying the display panel 112 so as to be disposed between the display panel 112 and the at least one eye 118 of a user. Cross view 122 depicts a cross-section view along line A-A of the beam steering assembly 120 overlying the display panel 112. The beam steering assembly 120 includes a stack of one or more optical beam steering elements, such as the two optical beam steering elements 124, 126 illustrated in FIG. 1, each optical beam steering element configured to replicate and displace incident light rays originating from the display panel 112.

The near-eye display system 100 also includes a display controller 130 to control the display panel 112 and, in some embodiments, a beam steering controller 132 to control the operation of the beam steering assembly 120. As also shown in FIG. 1, the near-eye display system 100 also includes a rendering component 134 including a set of one or more processors, such as the illustrated central processing unit (CPU) 136 and graphics processing units (GPUs) 138, 140 and one or more storage components, such as system memory 142, to store software programs or other executable instructions that are accessed and executed by the processors 136, 138, 140 so as to manipulate the one or more of the processors 136, 138, 140 to perform various tasks as described herein. Such software programs include, for example, rendering program 144 comprising executable instructions for an optical beam steering and image rendering process, as described below.

In operation, the rendering component 134 receives rendering information 146 from a local or remote content source 148, where the rendering information 146 represents graphics data, video data, or other data representative of an object or scene that is the subject of imagery to be rendered and displayed at the display sub-system 102. Executing the rendering program 144, the CPU 136 uses the rendering information 146 to send drawing instructions to the GPUs 138, 140, which in turn utilize the drawing instructions to render, in parallel, a series of image frames 150 for display at the left-eye display 104 and a series of lightfield frames 152 for display at the right-eye display 106 using any of a variety of well-known VR/AR computational/lightfield rendering processes.

As described in greater detail herein, the beam steering assembly 120 laterally displaces, or “shifts” the position of pixels in the image frames 150, 152 to fill in non-emissive portions of the display panel 112. For example, in some embodiments, the beam steering assembly 120 shifts the position of successive images displayed at the display panel 112 so as to project to the user a super-resolution image or a higher-resolution lightfield due to the succession of images effectively being superimposed due to the visual persistence effect of the human visual system. In other embodiments, the beam steering assembly 120 replicates pixels of each given image and laterally displaces the replicated pixels so as to project an image with pixels of a perceived larger size (e.g., due to increased effective pixel count) that conceals the non-emissive space between pixels. It will be appreciated that although described in the context of the near-eye display system 100, the beam steering described herein may be used for any type of VR or AR system (e.g., conventional magnifier displays, computational displays, see-through displays, and the like).

FIG. 2 illustrates a cross-section view of an implementation 200 of the near-eye display system 100 for providing super-resolution imagery to the eye 118 of the user in accordance with at least one embodiment of the present disclosure. In this example, the display panel 112 comprises an array of pixels, which typically are arranged as an interwoven pattern of sub-pixels of different colors, such as red, green, and blue (RGB) sub-pixels, and wherein the spatial persistence effects of human vision result in adjacent sub-pixels of different colors to be perceived as a single pixel having a color represented by a blend of the adjacent sub-pixels and their respective intensities. For ease of illustration, the display panel 112 is not depicted to scale, and is depicted as having only five sub-pixels in the cross-section (sub-pixels 202, 204, 206, 208, 210), whereas a typical display would have hundreds or thousands of sub-pixels along the cross-section, and thus it will be appreciated that the dimensions of the sub-pixels 202-210, and the non-emissive space in between the sub-pixels (e.g., non-emissive space 212 between sub-pixels 206 and 208) is significantly exaggerated relative to the other components of the implementation 200.

Further, to aid in illustration of the operation of the beam steering assembly 120, the implementation 200 of FIG. 2 illustrates the beam steering assembly 120 as having only a single optical beam steering element 214. Moreover, in FIG. 2, the user's eye 118 is depicted as a lens 216 representing the lens of the eye 118 and a panel 218 representing the retinal plane of the eye 118. As such, the panel 218 is also referred to herein as “retina 218.” Further, the implementation 200 includes a magnifier lens assembly 220 (not shown in FIG. 1 for ease of illustration) overlaying the display panel 112 such as to be disposed between the optical beam steering element 214 and the eye 118 of the user. Although illustrated in FIG. 2 to be a single lens, in other embodiments, the magnifier lens assembly 220 includes a lenslet array (not shown) with each lenslet focusing a corresponding region of the display panel 112 onto the lens 216 of the eye. It also should be noted that while FIG. 2 depicts an optical configuration with a single lens and the optical beam steering element 214 between the display panel 112 and the eye 118, in a typical implementation the optical system may comprise a larger number of lenses, prisms, or other optical elements between the display panel 112 and the eye 118.

As shown, the optical beam steering element 214 is configured to replicate light originating from sub-pixel 206 and displace the replicated sub-pixel such that the eye 118 perceives the replicated sub-pixel as originating from the non-emissive space 212 between sub-pixels 206 and 208, and thus create a perception of a display having an effective resolution of approximately twice the actual resolution of the display panel 112. To illustrate, in one embodiment, the beam steering controller 132 of FIG. 1 at time t₀ deactivates the beam steering element 214 and the display controller 130 scans in a first image for display by the display panel 112. The resulting light output by sub-pixel 206 for the first image is directed to a display-panel-facing surface of the beam steering element 214. Because the beam steering element 214 is deactivated at time t₀, the incident light is passed through the beam steering element 214 without lateral displacement to the user's eye 118, whereupon the lens 216 of the eye 118 focuses the light on the retina 218 at position 222 (with light from the other sub-pixels 202-204 and 208-210 taking corresponding paths).

Subsequently, at time t₁, the beam steering controller 132 of FIG. 1 activates the beam steering element 214, which configures the beam steering element 214 to laterally displace incident light (e.g., two-dimensional shift of incident light in the X- and/or Y-axis directions of FIG. 2). The display controller 130 scans in a second image for display by the display panel, and the resulting light output by sub-pixel 206 for the second image is directed to the display-panel-facing surface of the beam steering element 214. Because the beam steering element 214 is activated at time t₁, the incident light is laterally displaced after passing through the beam steering element 214. The laterally-displaced light is passed to the user's eye 118, whereupon the lens 216 of the eye 118 focuses the light on the retina 218 at position 224. The eye 118 perceives light at position 224 as originating from the non-emissive space 212 between sub-pixels 206 and 208 (although the light actually originated from sub-pixel 206). The lateral displacement of incident light at the beam steering element 214 results in presenting sub-pixels of the second image at positions where non-emissive spaces would have been perceived as black space by the eye 118 from the display of the first image at time t₀. Thus, if the first image at time t₀ and the second image at time t₁ are displayed in quick succession (i.e., within the visual persistence interval of the human eye, which is approximately 10 ms), the human visual system perceives the first and second images to be overlapping. That is, in this example, the lateral displacement introduced to the light of the second image has the result of presenting the sub-pixels of the second image where black spaces would have appeared to the eye 118 from the display of the first image, and thus the sub-pixels of the second image appear to the eye 118 to occupy black spaces associated with non-emissive portions of the display panel 112 for the first image.

The second image at time t₁, in some embodiments, has the same visual content as the first image at time t₀. In such embodiments, the eye 118 perceives the two images as overlapping in a single image of the same resolution of the first and second images (i.e., at native resolution of the display panel 112) but with larger perceived pixels that fill in the black space associated with non-emissive portions of the display panel 112, and thus reduce or eliminate the screen-door effect that would otherwise be visible to the eye 118. In other embodiments, the second image at time t₁ has different visual content than the first image at time t₀. In such embodiments, the eye 118 perceives the two images as overlapping in a single super-resolution image with visual content of the second image filling in the black space associated with non-emissive portions of the display panel 112. This reduces or eliminates the user's ability to perceive these non-emissive portions of the display panel 112, thereby creating a perception of a display having an effective resolution of approximately twice the actual resolution of the display panel 112.

It should be noted that although the implementation 200 of the near-eye display system 100 in FIG. 2 depicts a beam steering assembly having a single beam steering element 214 for lateral light displacement, as noted above the beam steering assembly 120 may employ a stack of multiple beam steering elements (e.g., beam steering elements 124, 126 of FIG. 1) of differing configurations so as to provide multiple different lateral displacements, and thus provide the option to shift multiple successive images in different directions. For example, assuming the stack uses beam steering elements having a replication factor of two (e.g., beam steering element 214 of FIG. 2 that passes incident light to two different locations as either laterally displaced or not laterally displaced based on two corresponding states of the beam steering element 214, activated or deactivated), a stack of four beam steering elements allows for the replication and steering of each sub-pixel of the display panel to four different positions (i.e., three laterally displaced positions plus one original sub-pixel position in which all four beam steering elements are deactivated so that light passes through without any lateral displacement).

It should further be noted that although the example of FIG. 2 is described in the context of a beam steering element 214 having a replication factor of two (i.e., deactivated to pass through without any lateral displacement or activated to replicate a sub-pixel for shifting to another position), other embodiments may employ beam steering elements having multiple different states. For example, instead of using a stack of four beam steering elements that each have a replication factor of two, a single beam steering element (not shown) having a replication factor of four may be controlled by beam steering controller 132 of FIG. 1 to switch between four different states that allow for the replication and steering of each sub-pixel of the display panel to four different positions (i.e., three laterally displaced positions plus one original sub-pixel position in which all four beam steering elements are deactivated so that light passes through without any lateral displacement).

In some embodiments, an amount of screen door effect perception (i.e., metric of screen door effect severity) is represented by the equation: MTF(u)*CSF(u) for all spatial frequencies u, where MTF represents a Modulation Transfer Function specifying how different spatial frequencies are handled by the optics of a system (e.g., the near-eye display system 100) and CSF represents a Contrast Sensitivity Function representing the eye's ability to discern between luminances of different levels in a static image. The product of eye's contrast sensitivity (i.e., how sensitive the eye is to certain spatial frequencies, which turns out to be very sensitive to screen door frequency) and the spatial frequency content of pattern produced with replication provides a system transfer function in which the larger the transfer function is (for that specific spatial frequency u), the more screen door will be perceived. Accordingly, reduction of the system transfer function can be represented by an optimization metric as provided by equation (1) below:

$\begin{matrix} {\min\limits_{d,\theta}\frac{\int_{u_{\min}}^{u_{\max}}{{{PTF}\left( {u,d,\theta} \right)}{{CSF}(u)}{du}}}{\int_{u_{\min}}^{u_{\max}}{{{PTF}\left( {u,0,0} \right)}{{CSF}(u)}{du}}}} & (1) \end{matrix}$ where u represents spatial frequency, d represents possible lateral displacement between replication spots, and θ represents rotation of replication/beam steering elements. The product of the equation provides a metric of how much screen door effect is perceivable after stacking a number N of beam steering elements. For example, based on equation (1) for a beam steering element (which can also be referred to as a “filter”) having a replication factor of two (such as described herein with respect to FIG. 2), one filter results in approximately 41% perceptibility of the screen door effect, two filters results in approximately 14% perceptibility of the screen door effect, three filters results in approximately 7.5% perceptibility of the screen door effect, and four filters results in approximately 3.1% perceptibility of the screen door effect. Accordingly, increasing the number of beam steering elements in a stack for the beam steering assembly generally reduces perceptibility of the screen door effect.

The beam steering assembly is implementable using any of a variety of suitable optical beam steering elements capable of sub-pixel-scale steering (i.e., steer replicated sub-pixels between positions based on states of the beam steering element). For example, FIG. 3 is a diagram illustrating a diffractive beam steering element in accordance with some embodiments. In the example of FIG. 3, a beam steering element 300 (e.g., one of the beam steering elements 124, 126 of FIG. 1 or beam steering element 214 of FIG. 2) is a stacked pair of gratings including a first grating 302 and a second grating 304 that splits and diffracts incident light into several beams traveling in different directions.

In some embodiments, the relationship between grating spacing and the angles of the incident and diffracted beams of light for beam steering element 300 is represented by equations (2) and (3):

$\begin{matrix} {{\theta = {\sin^{- 1}\frac{n\;\lambda}{D}}},} & (2) \\ {{t = \frac{d}{\tan\mspace{14mu}\theta}},} & (3) \end{matrix}$

where θ represents the diffractive angle between beams of diffracted light (i.e., angular deflection of the diffracted beam, n represents the order number, λ represents the wavelength of incident light, D represents the period of the gratings, t represents the distance between the gratings, and d represents the optical lateral displacement between the replicated sub-pixels. As discussed in more detail relative to FIG. 2, the lateral displacement distance d is less than a pixel to fill in the non-emissive portions between sub-pixels.

As shown, the first grating 302 of beam steering element 300 diffracts an incident beam of light 306 (e.g., light from a sub-pixel of the display panel) into the ±1 first orders. The second grating 304 of the grating pair further diffracts the light beams of ±1 first orders into the ±2 second orders and reverses the angular deflection of the diffracted beams such that light beams passing through the second grating 304 (and therefore leaving the beam steering element 300) has a direction matching the incidence angle of the incident beam of light 306 from sub-pixels of the display panel. In this manner, the beam steering element 300 replicates the original incident beam of light 306 and laterally displaces the replicated beams. Various amplitude or phase gratings may be utilized for diffracting the incident light beam and then reversing the angular deflection without departing from the scope of this disclosure. Further, the gratings may be designed for single or multiple diffraction orders to reduce thickness of the beam steering element.

In some embodiments, the relative spot intensities (i.e. diffraction efficiency) of spots (e.g., replicated beams of light) replicated by beam steering element 300 is represented by equation (4): sin c(n*w/D)²  (4) where n represents diffraction order number, w/D is the open fraction of the grating, and sin c(x)=sin(π*x)/(π*x). Accordingly, the intensity of the replicated spots may be adjusted based on the open fraction of gratings in beam steering element 300.

In another embodiment, FIG. 4 is a diagram illustrating a refractive beam steering element in accordance with some embodiments. In the example of FIG. 4, a beam steering element 400 (e.g., one of the beam steering elements 124, 126 of FIG. 1 or beam steering element 214 of FIG. 2) is a stacked pair of prisms including a first prism 402 and a second prism 404 that refracts incident light into several beams traveling in different directions. As shown, the first prism 402 angularly disperses an incident beam of white light 406 from the display panel 112 into three angularly-deviated rays. As the refractive index of prisms varies with the wavelength (i.e., color) of light, rays of different colors will be refracted differently and leave the first prism 402, thereby separating the incident beam of white light 406 into red, green, and blue rays. The red ray R has a longer wavelength than the green ray G and the blue ray B, and therefore leaves the first prism 402 with less angular deviation relative to the incident beam of white light 406 than the other rays. Similarly, the green ray G has a longer wavelength than the blue ray B, and therefore leaves the first prism 402 with less angular deviation relative to the incident beam of white light 406 than the blue ray B.

As shown, the second prism 404 receives the three angularly-deviated rays from the first prism 402 and reverses the angular deviations such that the rays leaving the second prism 404 (and therefore leaving the beam steering element 400) have red, green, and blue colored rays displaced laterally while having a direction matching the incidence angle of the incident beam of white light 406. In this manner, the beam steering element 400 spreads out or changes the location of pixels at a sub-pixel scale.

FIG. 5 a diagram illustrating another refractive beam steering element in accordance with some embodiments. In the example of FIG. 5, a beam steering element 500 (e.g., one of the beam steering elements 124, 126 of FIG. 1 or beam steering element 214 of FIG. 2) includes a liquid crystal cell 502 having liquid crystal molecules 504 oriented such as to form a birefringent material having a refractive index that depends on the polarization and propagation direction of light. As shown, the liquid crystal molecules 504 are oriented to have their symmetry axes at 45 degrees relative to the substrate plane. Accordingly, due to the double refraction phenomenon whereby a ray of incident light is split based on polarization into two rays taking slightly different paths, an incident beam of unpolarized light 506 is split into two rays 508, 510 and steered to one of two deflection angles, depending on polarization state.

For the incident beam of unpolarized light 506, a first ray 508 having a first polarization state (e.g., light whose polarization is perpendicular to the optic axis of the liquid crystal cell 502, referred to as “ordinary axis oriented”) passes through the liquid crystal cell 502 without deflection. The second ray 510 having a second polarization state (e.g., light whose polarization is in the direction of the optic axis of the liquid crystal cell 502, referred to as “extraordinary axis oriented”) is deflected and is passed with a lateral displacement d.

In some embodiments, the beam steering element 500 includes liquid crystal molecules 504 that are oriented as illustrated in FIG. 5 and polymerized such that the liquid crystal molecules 504 are linked to be static in that configuration, thereby forming a beam replication assembly. In other embodiments, the beam steering element 500 further includes a polarization switch (not shown) stacked on top of the polymerized liquid crystal cell that switches polarization between two values so that the liquid crystal molecules 504 only received polarized light (rather than the beam of unpolarized light 506 illustrated in FIG. 5). Accordingly, depending on the polarization of incident light, the incoming polarized light is either passed through or deviated (rather than passing both rays 508, 510 as illustrated in FIG. 5).

It should be noted that while embodiments implementing various beam steering elements (such as the beam steering elements of FIGS. 3-5 and 8-9) are described herein for illustrative purposes, other suitable beam steering elements capable of lateral (i.e., not angular) sub-pixel shifts may be implemented in place of the beam steering elements described herein unless otherwise noted.

FIG. 6 illustrates an example method 600 of operation of the near-eye display system 100 for display of super-resolution imagery in accordance with various embodiments. As described above relative to FIGS. 1-2, the near-eye display system 100 takes advantage of the visual persistence effect to provide a time-multiplex display of shifted imagery so that either a series of images is perceived by the user as either a single super-resolution image or a native-resolution image with effectively larger pixels that conceal the non-emissive portions of the display panel 112. The method 600 illustrates one iteration of the process for rendering and displaying an image for one of the left-eye display 104 or right-eye display 106, and thus the illustrated process is repeatedly performed in parallel for each of the displays 104, 106 to generate and display a different stream or sequence of frames for each eye at different points in time, and thus provide a 3D, autostereoscopic VR or AR experience to the user.

The method 600 initiates at block 602 with determining a display image to be generated and displayed at the display panel 112. In some embodiments, the rendering component 134 identifies the image content to be displayed to the corresponding eye of the user as a frame. In at least one embodiment, the rendering component 134 receives pose data from various pose-related sensors, such as a gyroscope, accelerometer, magnetometer, Global Positioning System (GPS) sensor, and the like to determines a current pose of the apparatus 108 (e.g., HMD) used to mount the displays 104, 106 near the user's eyes. From this pose data, the CPU 136, executing the rendering program 144, can determine a corresponding current viewpoint of the subject scene or object, and from this viewpoint and graphical and spatial descriptions of the scene or object provided as rendering information 146, determine the imagery to be rendered.

At block 604, the rendering program 144 manipulates the CPU 136 to sample the source image and generate a first array of pixels representing imagery to be rendered (e.g., as determined in block 602). The generated first array of pixels is subsequently transmitted to the display panel 112 to be displayed.

At block 606, the beam steering controller 132 configures the beam steering assembly 120 to be in a first configuration state while the display controller 130 controls the display panel 112 facing the beam steering assembly 120 to display the first array of pixels generated in block 604. In some embodiments, such as described above relative to time t₀ in FIG. 2, the first configuration state of the beam steering assembly is a deactivated state in which the optical beam steering element 214 allows the first array of pixels to be passed without any lateral displacements. In other embodiments, the first configuration state of the beam steering assembly laterally displaces the first array of pixels such that they are not laterally aligned with the original optical path between the display panel 112 and the beam steering assembly 120. Accordingly, the beam steering assembly, while in the first configuration state, imparts a first lateral displacement to the first array of pixels.

As explained above, for various beam steering devices, the switching between configuration states for the beam steering assembly typically includes activating or deactivating a particular combination of stages of the stack of beam steering elements comprising the beam steering assembly, such that the array of pixels leaving the beam steering assembly is laterally shifted based on the configuration state. Note that the process of block 606 may be performed concurrently with the corresponding image generation at block 604.

At block 608, the rendering program 144 manipulates the CPU 136 to sample the source image and generate a second array of pixels representing imagery to be rendered (e.g., as determined in block 602). The generated second array of pixels is subsequently transmitted to the display panel 112 to be displayed.

At block 610, the beam steering controller 132 configures the beam steering assembly 120 to be in a second configuration state while the display controller 130 controls the display panel 112 facing the beam steering assembly 120 to display the second array of pixels generated in block 608. In some embodiments, such as described above relative to time t₁ in FIG. 2, the second configuration state of the beam steering assembly is an activated state in which the optical beam steering element 214 laterally displaces the second array of pixels such that they are not laterally aligned with first array of pixels.

As explained above, for various beam steering devices, the switching between configuration states for the beam steering assembly typically includes activating or deactivating a particular combination of stages of the stack of beam steering elements comprising the beam steering assembly, such that the array of pixels leaving the beam steering assembly is laterally shifted based on the configuration state. Note that the process of block 608 may be performed concurrently with the corresponding image generation at block 610.

At block 612, the display controller 130 instructs the display panel to display the first and second array of pixels (e.g., as generated from blocks 604-610) within a visual perception interval so that the first and second first and second array of pixels are perceived by a user to be a single image with an effective resolution that is higher than a native resolution of the display panel 112, thereby presenting a super-resolution image.

It should be noted that although the method 600 of FIG. 6 is described in the context of only combining two arrays of pixels that are laterally shifted to each other to generate a super-resolution image, those skilled in the art will recognize that the number and rate of iterations of the processes of blocks 604-610 may be varied increase the number of laterally shifted images to be displayed by display panel 112 during the visual persistence interval of the human eye. For example, assuming the beam steering assembly 120 includes a stack of multiple different beam steering elements (e.g., beam steering elements 124, 126 of FIG. 1) with different configuration states, the processes of blocks 604-608 are repeated for each of the different configuration states so that multiple arrays of pixels that are laterally shifted relative to each other may be generated and displayed so as to be perceived as a single super-resolution image by the user. Alternatively, rather than resampling the source image between each lateral displacement of pixels, the same array of pixels can be shifted across the various configuration states and displayed so as to be perceived as a single standard-resolution image with reduced screen-door effect by the user.

As demonstrated above, the various optical beam steering assemblies described may be advantageously used to leverage the visual persistence effect of the human visual system to provide dynamically time-multiplexed, spatially shifted images that are perceived by a user as super-resolution images or native-resolution images with reduced perception of non-emissive portions of the display. Additionally, in other embodiments, the optical beam steering assemblies described may be used to passively replicate (i.e., without sending control voltages and changing states of the beam steering assemblies) and spatially shift incident light beams coming from the display panel to provide native-resolution images with reduced perception of non-emissive portions of the display.

It will be appreciated that other embodiments provide for passive super-resolution without any time-multiplexing of images. FIG. 7 is a diagram illustrating a method of generating passive super-resolution images in accordance with some embodiments. As shown, a first image 702 includes a plurality of pixels (with only four pixels 704, 706, 708, 710 shown for ease of illustration). A second image 712 provides the same content data (e.g., pixels 704, 706, 708, 710) as the first image 702, but is laterally shifted in position relative to the first image 702.

For example, in some embodiments, the first image 702 and the second image 712 are generated by presenting unpolarized light from a display screen to the beam steering element 500 of FIG. 5. For the incident unpolarized light, a first set of light rays having a first polarization state (e.g., light whose polarization is perpendicular to the optic axis of the beam steering element 500) passes through without deflection, thereby providing the first image 702. Additionally, for the same incident unpolarized light, a second set of light rays having a second polarization state (e.g., light whose polarization is in the direction of the optic axis of the beam steering element 500) is deflected and passed through with a lateral displacement d of a sub-pixel distance. In this example, the lateral displacement d is half a pixel in the x-axis direction and half a pixel in the y-axis direction, thereby diagonally shifting each of the pixels by half a pixel for the second image 712.

The first image 702 is overlaid with one or more sub-pixel shifted copies of itself (e.g., the second image 712) to generate a summed image 714 which is perceivable as having improved resolution relative to that of the first image 702 and the second image 712. It will be appreciated that depending on the overlap, certain sub-pixel portions of the summed image 714 gets contributions from the same pixel value. For example, the sub-pixel portion 716 provides image data that is provided only by the value of pixel 704. Other sub-pixel portions of the summed image 714 gets contributions from multiple different pixel values. For example, the sub-pixel portion 716 provides image data that is provided by both the values of pixel 704 and pixel 706. In this manner, the effective resolution of the perceived image (i.e., summed image 714) is increased without requiring time-multiplexing of images or coordinating the rendering of images with varying the states of beam steering elements.

FIG. 8 is a diagram illustrating a top-down view of a birefringent beam steering element in accordance with some embodiments. In the example of FIG. 8, the beam steering element 800 (e.g., one of the beam steering elements 124, 126 of FIG. 1 or beam steering element 214 of FIG. 2) is a layer of birefringent material that is tilted relative to a planar axis 802. As defined herein, the planar axis 802 represents a longitudinal axis along which the beam steering element 800 would be oriented if the beam steering element were parallel to the display panel 112.

In some embodiments, the layer of birefringent material of the beam steering element 800 is a birefringent plate 800 including a stretched polymer plate. Many polymers have a polarizability anisotropy or are inherently isotropic due to their three-dimensional chemical structures, and as such do not show birefringence in an unstressed state. In a completely amorphous state, polarizability anisotropies for repeating units are compensated by each other because the polymer molecular chains are randomly oriented. As a result, the polymer macroscopically becomes optically isotropic and exhibits no birefringence. The polymer, however, exhibits birefringence when the polymer molecular chains are oriented by stress. For example, when the polymer is subjected to stresses from extrusion, stretching and injection, blow molding processes, or post manufacturing unintentional damage, the induced stress shows up as birefringence in the finished materials.

It should be noted that while embodiments implementing various beam steering elements as stretched polymer plates or stretched polymer films are described herein for illustrative purposes, other suitable birefringent beam steering elements capable of lateral (i.e., not angular) sub-pixel shifts may be implemented in place of the beam steering elements described herein unless otherwise noted. For example, various birefringent materials formed from stress and strain due to external forces and/or deformation acting on materials that are not naturally birefringent, such as deformed glass, plastic lenses, and stressed polymer castings, may be used without departing from the scope of this disclosure.

As shown in FIG. 8, the birefringent plate 800 includes an in-plane symmetry axis 804 that is parallel to the longitudinal length of the birefringent plate 800. For each input ray of light 806, the birefringent plate 800 generates two output rays of light 808, 810 by replicating the input ray of light 806. Thus, both of the replicated rays of light (i.e., output rays of light 808, 810) represent the same visual content as the input ray of light 806 incident on the beam steering assembly. One of the output rays of light 808 is passed through the birefringent plate 800 along substantially the same direction as an optical path 812 of the incident, input ray of light 806 (i.e., the light ray incident on the beam steering assembly). The other output ray of light 810 is a replicated ray of the incident, input ray of light 806 that is laterally displaced (e.g., two-dimensional shift of incident light in the X- and/or Y-axis directions of FIG. 8) relative to the input ray of light 806 and the output ray of light 808. It should be noted that the birefringent plate 800 causes lateral ray displacement but does not cause angular displacement of light rays. That is, a light ray emitted from the display panel 112 does not undergo a change in the angular direction of its light path (i.e., the optical path of the light beam incident on the beam steering element 800). Thus, the beam steering element (i.e., birefringent plate 800) replicates pixels of each given image and laterally displaces the replicated pixels so as to project an image with pixels of a perceived larger size (e.g., due to increased effective pixel count) that conceals the non-emissive space of display panel 112 between pixels.

In some embodiments, the beam steering element 800 is coupled to an actuator 814 configured to rotate the beam steering element 800 around the X-axis, Y-axis, and/or Z-axis such as to change the relative angle between the in-plane symmetry axis 804 of the birefringent plate and the planar axis 802. In various embodiments, the actuator 814 is controlled by the rendering component 134 to change the amount of lateral displacement between the two output rays of light 808, 810. In various embodiments, the actuator 814 may include optomechanical actuators such as piezo-electric, voice-coil, or electro-active polymer actuators. Although described here in the context of optomechanical actuators, those skilled in the art will recognize that any mechanical actuator capable of physically rotating the beam steering element 800 may be used without departing from the scope of this disclosure.

In various embodiments, a distance Δx by which a replicated ray is laterally displaced is represented by the following equations:

$\begin{matrix} {{\Delta\; x} = {\alpha*\Delta\; z}} & (5) \\ {\alpha = {\theta - {\arctan\left( {\frac{n_{o}^{2}}{n_{e}^{2}}\tan\mspace{14mu}\theta} \right)}}} & (6) \end{matrix}$ where Δz is the thickness of the birefringent plate 800 and a is the angular deviation of the replicated ray inside the birefringent plate 800, which after exiting turns into a lateral displacement of Δx. θ represents a tilt angle between the in-plane symmetry axis 804 of the birefringent plate and the angle of the incoming input ray of light 806 incident on the beam steering assembly (or the planar axis 802). Generally, a distance of max displacement is achieved when the in-plane symmetry axis 804 of the birefringent plate is at 45 degrees relative to the incoming ray. At 90 degrees, zero displacement of the replicated ray occurs.

It should be noted that although the example of FIG. 8 is described in the context of a beam steering element 800 having a replication factor of two (i.e., replicate an incoming input ray and sub-pixel lateral shifting to another position), other embodiments may employ a stack of birefringent plate beam steering elements to increase the amount of ray multiplication. For example, as described below in more detail relative to FIG. 9, instead of using a single tilted birefringent plate, by using a stack of two tilted birefringent plates that each have a replication factor of two, a single beam steering element having a replication factor of four may be controlled by beam steering controller 132 and/or the rendering component 134 of FIG. 1 to allow for the replication and steering of each sub-pixel of the display panel to four different positions (i.e., three laterally displaced positions plus one original sub-pixel position).

FIG. 9 is a diagram illustrating a top-down view of another birefringent beam steering element in accordance with some embodiments. In the example of FIG. 9, the beam steering element 900 (e.g., one of the beam steering elements 124, 126 of FIG. 1 or beam steering element 214 of FIG. 2) is tilted relative to the planar axis 902 and includes a stack of birefringent plates including a first birefringent plate 904 and a second birefringent plate 906. Similar to that of FIG. 8, the planar axis 902 represents a longitudinal axis along which the beam steering element 900 would oriented if the beam steering element were parallel to the display panel 112. The beam steering element 900 further includes a quarter wave plate 908 positioned between the first birefringent plate 904 and the second birefringent plate 906.

In various embodiments, each layer of birefringent material of the beam steering element 900 (e.g., the first birefringent plate 904 and the second birefringent plate 906) is a stretched polymer plate. However, while embodiments implementing various beam steering elements as stretched polymer plates or stretched polymer films are described herein for illustrative purposes, other suitable birefringent polymer beam steering elements capable of lateral (i.e., not angular) sub-pixel shifts may be implemented in place of the beam steering elements described herein unless otherwise noted. For example, various birefringent materials formed from stress and strain due to external forces and/or deformation acting on materials that are not naturally birefringent, such as deformed glass, plastic lenses, and stressed polymer castings, may be used without departing from the scope of this disclosure.

As shown in FIG. 9, the first birefringent plate 904 includes an in-plane symmetry axis 910 that is parallel to the longitudinal length of the first birefringent plate 904. For each input ray of light 914, the first birefringent plate 904 generates two output rays of light (not shown). One of the output rays of light is passed through the first birefringent plate 904 along substantially the same direction as an optical path of the incident, input ray of light 914. The other output ray of light is a replicated ray of the incident, input ray of light 914 that is laterally displaced (e.g., two-dimensional shift of incident light in the X- and/or Y-axis directions of FIG. 9) relative to the input ray of light 914. Thus, both of the replicated rays of light (i.e., output rays of light output from the first birefringent plate 904) represent the same visual content as the input ray of light 914 incident on the beam steering assembly. The quarter wave plate 908 polarizes those two output rays of light (i.e., replicated rays resulting from the input ray of light 914 passing through the first birefringent plate 904) to generate light rays having circular polarization prior to the light rays reaching the second birefringent plate 906. If light incident on the birefringent plates is not circularly polarized, spot multiplication (i.e., light ray replication) does not occur.

For each input ray of light, the second birefringent plate 906 also generates two output rays of light (not shown). Accordingly, the polarized two output rays of light (i.e., replicated rays resulting from the input ray of light 914 passing through the first birefringent plate 904 and the quarter wave plate 908) result in a total of at least four output rays of light 916. Thus, the replicated rays of light (i.e., output rays of light 916) represent the same visual content as the input ray of light 914 incident on the beam steering assembly. One of the output rays of light 916 is passed through the beam steering element 900 along substantially the same direction as an optical path of the incident, input ray of light 914 (i.e., the light ray incident on the beam steering assembly). The other three output rays of light 916 are laterally displaced relative to the optical path. In this manner, the beam steering element 900 replicates pixels of each given image and laterally displaces the replicated pixels so as to project an image with pixels of a perceived larger size (e.g., due to increased effective pixel count) that conceals the non-emissive space of display panel 112 between pixels.

In some embodiments, the beam steering element 900 is coupled to an actuator 918 configured to rotate the beam steering element 900 around the X-axis, Y-axis, and/or Z-axis such as to change the relative angle between the in-plane symmetry axes 910, 912 of the beam steering element 900 and the planar axis 902. In various embodiments, the actuator 918 is controlled by the rendering component 134 to change the amount of lateral displacement between the four output rays of light 916. In various embodiments, the actuator 918 may include optomechanical actuators such as piezo-electric, voice-coil, or electro-active polymer actuators. Although described here in the context of optomechanical actuators, those skilled in the art will recognize that any mechanical actuator capable of physically rotating the beam steering element 900 may be used without departing from the scope of this disclosure.

In some embodiments, certain aspects of the techniques described above may implemented by one or more processors of a processing system executing software. The software comprises one or more sets of executable instructions stored or otherwise tangibly embodied on a non-transitory computer readable storage medium. The software can include the instructions and certain data that, when executed by the one or more processors, manipulate the one or more processors to perform one or more aspects of the techniques described above. The non-transitory computer readable storage medium can include, for example, a magnetic or optical disk storage device, solid state storage devices such as Flash memory, a cache, random access memory (RAM) or other non-volatile memory device or devices, and the like. The executable instructions stored on the non-transitory computer readable storage medium may be in source code, assembly language code, object code, or other instruction format that is interpreted or otherwise executable by one or more processors.

A computer readable storage medium may include any storage medium, or combination of storage media, accessible by a computer system during use to provide instructions and/or data to the computer system. Such storage media can include, but is not limited to, optical media (e.g., compact disc (CD), digital versatile disc (DVD), Blu-Ray disc), magnetic media (e.g., floppy disc, magnetic tape, or magnetic hard drive), volatile memory (e.g., random access memory (RAM) or cache), non-volatile memory (e.g., read-only memory (ROM) or Flash memory), or microelectromechanical systems (MEMS)-based storage media. The computer readable storage medium may be embedded in the computing system (e.g., system RAM or ROM), fixedly attached to the computing system (e.g., a magnetic hard drive), removably attached to the computing system (e.g., an optical disc or Universal Serial Bus (USB)-based Flash memory), or coupled to the computer system via a wired or wireless network (e.g., network accessible storage (NAS)).

Note that not all of the activities or elements described above in the general description are required, that a portion of a specific activity or device may not be required, and that one or more further activities may be performed, or elements included, in addition to those described. Still further, the order in which activities are listed are not necessarily the order in which they are performed. Also, the concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present disclosure as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present disclosure.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims. Moreover, the particular embodiments disclosed above are illustrative only, as the disclosed subject matter may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. No limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the disclosed subject matter. Accordingly, the protection sought herein is as set forth in the claims below. 

What is claimed is:
 1. A near-eye display system, comprising: a display panel configured to display a sequence of images; and a beam steering assembly facing the display panel, the beam steering assembly including a first birefringent plate configurable to replicate a light ray incident on the beam steering assembly, wherein the replicated light ray is laterally shifted by a distance, based on a tilt angle of the beam steering assembly, relative to an optical path of the light ray incident on the beam steering assembly while maintaining a same angular direction as the light ray.
 2. The near-eye display system of claim 1, wherein: an in-plane symmetry axis of the first birefringent plate is tilted relative to the optical path of the light ray incident on the beam steering assembly.
 3. The near-eye display system of claim 1, further comprising: an actuator coupled to the beam steering assembly, the actuator to change the tilt angle between the beam steering assembly and the optical path of the light ray incident on the beam steering assembly.
 4. The near-eye display system of claim 3, further comprising: a display controller coupled to the display panel, the display controller to drive the display panel to display the sequence of images; and a beam steering controller coupled to the actuator, the beam steering controller to instruct the actuator to impart a different tilt angle between the beam steering assembly and the optical path of the light ray incident on the beam steering assembly, wherein the different tilt angle changes a lateral shift for light rays replicated by the beam steering assembly.
 5. The near-eye display system of claim 1, wherein: the beam steering assembly comprises a stacked pair of birefringent plates including the first birefringent plate and a second birefringent plate, and further wherein each of the first and second birefringent plates replicates incident light rays.
 6. The near-eye display system of claim 5, further comprising: a quarter wave plate positioned between the first birefringent plate and the second birefringent plate, wherein the quarter wave plate polarizes light rays output from the first birefringent plate prior to passing the polarized light rays to the second birefringent plate.
 7. The near-eye display system of claim 5, wherein: the beam steering assembly outputs at least four light rays for each light ray incident on the beam steering assembly.
 8. The near-eye display system of claim 1, wherein the beam steering assembly is configured to output the replicated light ray that is laterally shifted and an additional replicated light ray that maintains a same optical path as the light ray incident on the beam steering assembly.
 9. The near-eye display system of claim 1, wherein the replicated light ray represents a same visual content as the light ray incident on the beam steering assembly so that each of the sequence of images is perceived by a user as having a resolution of the display panel and having pixels with an apparent size that is larger than an actual size of the pixels of the display panel.
 10. In a near-eye display system, a method comprising: positioning a beam steering assembly, including a first birefringent plate, at a first tilt angle so that the beam steering assembly is tilted relative to an optical path of a light ray incident on the beam steering assembly; and replicating the light ray incident on the beam steering assembly by passing the light ray through the first birefringent plate, wherein the replicated light ray is laterally shifted by a first distance, based on the first tilt angle, relative to the optical path of the light ray while maintaining a same angular direction as the light ray.
 11. The method of claim 10, further comprising: repositioning the beam steering assembly to a second tilt angle so that the beam steering assembly is tilted relative to the optical path of the light ray incident on the beam steering assembly; and replicating the light ray incident on the beam steering assembly by passing the light ray through the first birefringent plate, wherein the replicated light ray is laterally shifted by a second distance, based on the second tilt angle, relative to the optical path of the light ray.
 12. The method of claim 11, wherein: repositioning the beam steering assembly comprises controlling an actuator coupled to the beam steering assembly to change from the first tilt angle to the second tilt angle.
 13. The method of claim 10, further comprising: controlling a display panel facing the beam steering assembly to display a first image while the beam steering assembly is a first configuration state with the beam steering assembly positioned at the first tilt angle; and controlling the beam steering assembly to impart a first lateral shift for the first image.
 14. The method of claim 13, further comprising: controlling the display panel facing the beam steering assembly to display a second image; and signaling the beam steering assembly to enter a second configuration state with the beam steering assembly positioned at a second tilt angle to impart a second lateral shift for the second image.
 15. The method of claim 14, further comprising: controlling the display panel to display the first and second images within a visual perception interval so that the first and second images are perceptible as a single image with an effective resolution that is higher than a native resolution of the display panel.
 16. The method of claim 14, wherein: the first and second images contain a same visual content and which are displayed in a period of time less than a visual persistence interval so that the first and second images are perceptible as a single image having a resolution of the display panel and having pixels with an apparent size that is larger than an actual size of the pixels of the display panel.
 17. The method of claim 10, wherein: the beam steering assembly includes the first birefringent plate and a second birefringent plate, and the first tilt angle of the beam steering assembly replicates the light ray incident on the beam steering assembly into a plurality of laterally shifted beams, and wherein each of the plurality of laterally shifted beams includes a different lateral shift.
 18. The method of claim 17, further comprising: passing the plurality of laterally shifted beams for display so that the plurality of laterally shifted beams are perceptible as a single image having a resolution of a display panel facing the beam steering assembly and having pixels with an apparent size that is larger than an actual size of the pixels of the display panel.
 19. A rendering system, comprising: at least one processor; a beam steering assembly facing a display panel, the beam steering assembly including a first birefringent plate configurable to replicate a light ray incident on the beam steering assembly, wherein the replicated light ray is laterally shifted by a distance, based on a tilt angle of the beam steering assembly, relative to an optical path of the light ray incident on the beam steering assembly while maintaining a same angular direction as the light ray; and a storage component to store a set of executable instructions, the set of executable instructions configured to manipulate the at least one processor to: sample a source image to render a first image including a first array of pixels; resample the source image to render a second image comprising a second array of pixels; and signal a display controller coupled to the display panel to present both the first image and the second image in a period of time less than a visual persistence interval so that the first array of pixels and the second array of pixels are perceptible as a single image.
 20. The rendering system of claim 19, wherein the set of executable instructions are further configured to manipulate the at least one processor to: resample the source image to render a second image comprising a second array of pixels; and signal a display controller coupled to the display panel to present both the first image and the second image in a period of time less than a visual persistence interval so that the first and second arrays of pixels are perceptible as a single image.
 21. The rendering system of claim 19, wherein the first array of pixels are laterally shifted relative to the optical path by the beam steering assembly prior to presentation to a user. 